The present invention relates to an automatic gain controller and an automatic gain control method for outputting the input signal, whose level varies, in a manner that the input signal is made constant via feedback loop, and radio communications apparatus having the automatic gain control function.
The automatic gain control, typically abbreviated as AGC, has been implemented in a variety of signal processors. For example, in radio communications, the signal level of a received signal varies due to fading in a radio propagation path. Thus the receiving system of radio communications apparatus is equipped with an automatic gain control function in order to make constant the level of the received signal and to reduce demodulation errors.
In automatic gain control, it is desired that pull-in operation can be made in an early stage after power-on. For example, some of the radio communications apparatus that uses a battery as a power supply performs intermittent reception in order to prolong service life of the battery. In such radio communications apparatus, power-on/off is frequently repeated so that the request for reduction of the initial pull-in time is earnest.
As a technology for reducing the initial pull-in time, the xe2x80x9chigh-speed AGC circuitxe2x80x9d is described in the Japanese Patent Publication No. H11-88083. The xe2x80x9chigh-speed AGC circuitxe2x80x9d according to this conventional example maintains the AGC operation point by controlling the gain control signal of the amplifier via a pulse signal having an arbitrary pulse width at power-on, thus reducing the initial pull-in time.
However, for an aforementioned conventional automatic gain controller, a complicated control was required to reduce the initial pull-in time at power-on. Such a control was only realized by most of the related feature in a hardware configuration. This presented a problem of expansion of the circuit scale.
The invention, in view of the aforementioned circumstances, aims at providing an automatic gain controller and an automatic gain control method for reducing the initial pull-in time at power-on, and radio communications apparatus having the automatic gain control function.
An automatic gain controller according to the invention is characterized in that the automatic gain controller comprises variable gain amplifying means for variably amplifying an input signal based on a gain control signal to output a signal of a predetermined level, gain control signal generating means for generating an automatic gain control signal based on the difference between the level of the output signal of the variable gain amplifying means and a target value, sweep signal output means for outputting a sweep signal used for scanning across the minimum value and the maximum value of the variable gain range of the variable gain amplifying means, gain voltage value detecting means for detecting the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value, and gain control signal supplying means for supplying the sweep signal as a gain control signal to be supplied to the variable gain amplifying means in the initial stage of operation, supplying the control voltage value obtained when the level of the output signal has coincided with the target value after the sweep operation via the sweep signal, and supplying the automatic gain control signal that is based on the difference after output of the control voltage value.
Preferably, the gain control signal supplying means assumes completion of the sweep operation when the sweep signal has traversed across one and the other of the minimum value and the maximum value in the variable gain range, and outputs the control voltage value as the gain control signal on completion of the sweep operation. Or, the gain control signal supplying means stops the sweep operation when the level of the output signal has coincided with the target value, and outputs the control voltage value as the gain control signal on stoppage of the sweep operation.
Preferably, the automatic gain controller comprises start operation control means for determining that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has fallen within a predetermined control value range of the variable gain range of the variable gain amplifying means, and supplying the median of the control value range as the gain control signal to the variable gain amplifying means at the start of the next operation when the control voltage value has fallen within this control value range a predetermined number of times in succession.
Preferably, the automatic gain controller comprises sweep control means for determining that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has been biased to one side of the variable gain range of the variable gain amplifying means, and performing sweep operation in the direction opposite to the sweep direction of the sweep signal at the start of the next operation when the control voltage value has fallen within this biased control value range a predetermined number of times in succession.
An automatic gain control method according to the invention is an automatic gain control method for variably amplifying an input signal based on a gain control signal via the variable gain amplifying means to output a signal of a predetermined level, characterized in that the automatic gain control method comprises a sweep signal supplying step for supplying a sweep signal that scans across the minimum value and the maximum value of the variable gain range of the variable gain amplifying means in the initial stage of operation, a control voltage value supplying step for detecting the control voltage value of the sweep signal obtained when the level of the output signal of the variable gain amplifying means has coincided with the target value and supplying the control voltage value after the sweep operation via the sweep signal, and an automatic gain control signal supplying step for generating an automatic gain control signal based on the difference between the level of the output signal of the variable gain amplifying means and a target value and supplying the automatic gain control signal after output of the control voltage value.
Preferably, the sweep signal supplying step assumes completion of the sweep operation when the sweep signal has traversed across one and the other of the minimum value and the maximum value in the variable gain range, and outputs the control voltage value as the control voltage value supplying step. Or, the sweep signal supplying step stops the sweep operation when the level of the output signal has coincided with the target value, and supplies the control voltage value as the control voltage value supplying step on stoppage of the sweep operation.
Preferably, the automatic gain control method comprises a start operation control step for determining that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has fallen within a predetermined control value range of the variable gain range of the variable gain amplifying means, and supplying the median of the control value range as the gain control signal to the variable gain amplifying means at the start of the next operation when the control voltage value has fallen within this control value range a predetermined number of times in succession.
Preferably, the automatic gain control method comprises a sweep control step for determining that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has been biased to one side of the variable gain range of the variable gain amplifying means, and performing sweep operation in the direction opposite to the sweep direction of the sweep signal at the start of the next operation when the control voltage value has fallen within this biased control value range a predetermined number of times in succession.
Radio communications apparatus according to the invention is radio communications apparatus comprising an automatic gain control feature for variably amplifying an input signal based on a gain control signal via the variable gain amplifying means to output a signal of a predetermined level, characterized in that the radio communications apparatus comprises gain control signal generating means for generating an automatic gain control signal based on the difference between the level of the output signal of the variable gain amplifying means and a target value, sweep signal output means for outputting a sweep signal that scans across the minimum value and the maximum value of the variable gain range of the variable gain amplifying means, gain voltage value detecting means for detecting the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value, and gain control signal supplying means for supplying the sweep signal as a gain control signal to be supplied to the variable gain amplifying means in the initial stage of the operation, supplying the control voltage value obtained when the level of the output signal has coincided with the target value after the sweep operation via the sweep signal, and supplying the automatic gain control signal that is based on the difference after output of the control voltage value.
Preferably, radio communications apparatus comprises fading pitch detecting means for detecting the fading pitch of the input signal and start operation control means for determining that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has fallen within a predetermined control value range of the variable gain range of the variable gain amplifying means when the cycle of the detected fading pitch is shorter than a predetermined value, and supplying the median of the control value range as the gain control signal to the variable gain amplifying means at the start of the next operation when the control voltage value has fallen within this control value range a predetermined number of times in succession.
The invention supplies a sweep signal as a gain control signal to be supplied to variable gain amplifying means in the initial stage of operation, detects the control voltage value of the sweep signal obtained when the level of the output signal has coincided with a target value, supplies the control voltage value after the sweep operation, supplies an automatic gain control signal that is based on the difference between the level of the output signal and the target value, then starts and executes automatic gain control. This allows an early pull-in operation at the start of operation, generally at power-on, and allows execution to quickly shift to the primary automatic gain control via a closed loop. Thus it is possible to reduce the initial pull-in time at power-on via a simple configuration without expanding the circuit scale.
In this practice, more preferably, by reducing or making smaller the time constant of the circuit prior to sweep operation via a sweep signal in a level detection circuit such as a detecting circuit for detecting the level of an output signal, a faster pull-in operation is allowed and the accuracy of the automatic control at power-on is upgraded.
When automatic gain control is intermittently performed by turning on/off the power supply, it is determined that the control voltage value of a sweep signal obtained when the level of an output signal has coincided with a target value has fallen within a predetermined control value range of the variable gain range of variable gain amplifying means, and the median of the control value range is supplied to the variable gain amplifying means as a gain control signal at the start of the next operation or power-on in case the control voltage value has fallen within this control value range a predetermined number of times in succession. This further boosts the pull-in operation at the start of operation by using the median of the control value range when the control voltage value remains stable while automatic gain control is being performed intermittently several times.
When automatic gain control is performed intermittently by turning on/off the power supply, it is determined that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has been biased to one side of the variable gain range of the variable gain amplifying means, and sweep operation is performed in the direction opposite to the sweep direction of the sweep signal at the start of the next operation or power-on when the control voltage value has fallen within this biased control value range a predetermined number of times in succession. For example, in case the control voltage value has fallen within the control value range biased to the maximum value side of the variable gain range a predetermined number of times in succession while a sweep signal is used to scan from the minimum value to the maximum value of the variable gain range of the variable gain amplifying means, the sweep signal is used to scan from the maximum value to the minimum value at the next power-on to supply the sweep signal and to detect the control voltage value obtained when the level of the output signal has coincided with the target value. This further boosts the pull-in operation at the start of operation by reversing the sweep direction in case the sweep start voltage value is distant from the control voltage value as a convergence result obtained when automatic gain control is performed intermittently several times.
When automatic gain control is intermittently performed in the intermittent operation via radio communications apparatus, the fading pitch of an input signal or received signal is detected. Then it is determined that the control voltage value of the sweep signal obtained when the level of the output signal has coincided with the target value has fallen within a predetermined control value range of the variable gain range of the variable gain amplifying means, and the median of the control value range is supplied to the variable gain amplifying means as a gain control signal at the start of the next operation or power-on in case the control voltage value has fallen within this control value range a predetermined number of times in succession. This further boosts the pull-in operation at the start of operation by using the median of the control value range depending on the fading pitch of the reception signal, that is, in case the cycle of the fading pitch is short depending on the receiving state that varies with travel velocity.
In this practice, more preferably, the aforementioned sweep operation is performed at the start of operation in case the power-on cycle or operation cycle of automatic gain control is long or slow, and the median of the control value range is used to perform pull-in operation. This makes it more appropriately feasible to start automatic gain control.